1. Field of the Invention
The invention relates to a bicycle power train assembly, more particularly to a bicycle power train assembly which permits a further reduction in the force which is to be applied when climbing an uphill slope.
2. Description of the Related Art
Referring to FIG. 1, a conventional bicycle power train assembly is shown to comprise a pedal (1) which is used to rotate a crank axle (2) and a driving sprocket cluster (3). A driven sprocket cluster (5) is mounted on a rear wheel axle (4). A drive chain (6) is trained between the driving and driven sprocket clusters (3, 5). Front and rear derailleurs (7, 8) are provided to train the drive chain (6) on a selected sprocket of the sprocket clusters (3, 5).
Note that the smallest sprocket of the driving sprocket cluster (3) should not be too small so as to prevent the front derailleur (7) from latching onto the bicycle frame.
The bicycle power train assembly further includes a tension wheel (9) which is operated so as to compensate for the resulting difference in the tension of the drive chain (6) when the drive chain (6) is trained from one sprocket to another. Note that the largest sprocket of the driven sprocket cluster (5) should not be too large. Otherwise, the required length of the drive chain (6) becomes longer, making it difficult for the tension wheel (9) to maintain the drive chain (6) in tension when the drive chain (6) is trained on the smaller sprockets of the driving and driven sprocket clusters (3, 5).
Note that less force is required to move the bicycle forward if the drive chain (6) is trained on the smallest sprocket of the driving sprocket cluster (3). However, since the size of the smallest sprocket of the driving sprocket cluster (3) cannot be too small because of the above mentioned reason, a further reduction in the force which is to be applied when climbing an uphill slope is not possible.